Speaker
Description
The DAMA experiments have detected a modulating signal compatible with dark matter for 20 years with a combined significance of 12.9~$\sigma$. A result in tension for a spin independent WIMP with null results from large noble gas experiments. This is the motivation for SABRE (Sodium iodide with Active Background Rejection) South experiment. A NaI(Tl) based replication studies of the DAMA experiment, and the Southern Hemispheres first dark matter direct detection experiment. It is designed to test the DAMA modulation results the same NaI(Tl) crystal target readout by 14 Hamamatsu R11065 photomultiplier tubes (PMTs) with a 1~keV$_{\text{ee}}$ threshold.
This threshold corresponds to $\sim13$ detected photons, this makes separating genuine scintillation events from PMT noise difficult. Thus PMT noise is a significant component of the low energy background model that is difficult to include in time dependent background models as it cannot be modelled in Monte Carlo simulations. This makes accurate measurement of the low energy noise important for both understanding and minimising its contribution to the overall background.
This talk will report on the photomultiplier characterisation test bench developed for the crystal detector photomultipliers of SABRE South and preliminary results from the first test batch of PMTs. This includes studies of the single photon response, quantum efficiency, and dark noise. A specific focus is on correlated dark noise between two photomultipliers above the random coincidence rate, due to its significant contribution to the low energy background, we provide estimates of this effect also utilising studies of photomultipliers noise from underground measurements at LNGS. The results of the photomultiplier characterisation are crucial to model and understand the low energy performance of the SABRE South experiment. This is crucial to ensure that SABRE South can provide and accurate and untactful measurement of the DAMA signal.
